Hi marco,
I believe the convention is, in the order you have laid out-
circled roman numeral
roman numeral in parenthesis
roman numeral
circled arabic numerals
arabic numerals in parenthesis
arabic numerals
circled lower case roman numerals
lower case roman numerals in parenthesis
lower case roman numerals
A detailed description of this lettering and the convention for a.b.c waves can be found in Chapter 1 of Frost and Prechter's "Elliott Wave Principle."
Best to you!